A weighing module for a load cell that is to be installed in the weighing module is disclosed.
Weighing modules can be used in diverse fields of application, depending on the type of load cell being used and on the desired load range. Weighing modules with high-capacity load cells are used primarily to determine the weight and to weigh the contents of high-volume containers, silos, tanks, reactor vessels and/or reaction containers. The weighing of the contents can be accomplished by way of a differential weighing of the container in the empty condition and after it has been filled. Weighing modules of the type described herein can also be used under extreme ambient conditions such as for example in an open-air environment, in a technical facility or in a production plant.
Commercially available weighing modules include among others the models “Centerlign™” and “Flexmount™” by Mettler Toledo. The Centerlign™ device includes a beam-shaped load cell. The Flexmount™ device represents a weighing module with a beam-shaped weighing cell and has a lift-off safety feature. A weighing cell is arranged between two mounting devices which are designed so that the weighing module can be installed between a load and a supporting structure. Beam-shaped load cells are load cells with an elongated shape. One end of the beam-shaped load cell is immovably connected to the weighing module and the other end is arranged to allow displacement under load. Besides weighing modules with beam shaped load cells there are also modules with rocker pin load cells available.
A weighing module with a beam-shaped load cell is disclosed for example in EP 1 275 943 A2, wherein the load cell cooperates with a pin-shaped or ball-shaped force-transmitting element.
The conventional weighing modules are protected primarily against mechanical damage to the weighing module and/or to the load cell. They include lift-off safety devices and/or overload safety devices with the purpose of preventing a destructive separation of the mounting devices as well as preventing a destruction of the load cell for example under excessively heavy loads. The known prior art further includes a variety of means for the alignment and/or the limitation of the free play of the weighing module and in particular of the mounting devices in relation to the load cell and to each other.
Besides an incorrect alignment of the weighing module, there are also other factors that can have an influence on the weighing result. These factors include, among others, impact forces in a horizontal plane as a result of oscillations of the container caused by, for example, stirring mechanisms inside the container and temperature fluctuations and/or temperature changes which can occur on the one hand as a result of a change in the outside temperature and/or the room temperature, but also when the container to be weighed warms up and/or cools down. If the container to be weighed is heated or cooled, for example when a chemical reaction is carried out, the thermal expansion of the container can cause a change in the container dimensions.
A weighing module arrangement and/or the individual weighing modules should therefore have the capability of restricting oscillations of the weighing container in a horizontal plane while accommodating its thermal expansion and contraction as a result of a temperature change. The individual weighing modules should on the one hand be intrinsically rigid to allow them to carry the load of the container to be weighed and to restrict its oscillations, and they should on the other hand have sufficient mobility to allow unhindered expansion of the weighing container and absorb extraneous forces without compromising the proper function of the load cell and/or of the weighing module, and also without allowing the container to tip over.
To weigh large-volume containers one uses a weighing module arrangement with several weighing modules which differ from each other in their respective degrees of mobility. For example, one fixed module is used together with two or more modules that allow movement. The play of the weighing modules is often delimited by complex means which, for example, require an exact alignment or which cause friction forces to occur between the load cell and the means for delimiting the play. When friction forces are present, they can cause for example the application of extraneous side forces to the load cell, whereby the weighing accuracy is degraded, or an abrasion of material, whereby the function of the delimiting means can be altered.